i) Field of the Invention:
The present invention relates to a positional control apparatus for use in a machine tool, a measuring device or the like having a numerical control device hereinafter referred to as an NC device.
ii) Description of the Related Arts:
In a conventional positional control apparatus used for an NC device, a manual operation mode is provided for moving a turret position for an initial setup change by an operator, obtaining a tool offset or the like. In the manual operation mode, two position control methods are provided, that is, a first position control method in which a movable part can be quickly moved at a certain feeding speed determined by a feed override switch during pushing of a manual feed button even when a specific target position is undetermined, and a second position control method suitable for accurate minute feeding, in which a movable part can be moved by an amount which is the product of a pulse number generated by rotating a pulse handle and a certain moving amount determined by a turnover switch of a feed unit amount.
In FIG. 9, there is shown a conventional positional control apparatus in which a movable part can be quickly moved at a certain feeding speed determined by a feed override switch during pushing of a manual feed button in a manual operation mode. The positional control apparatus includes a moving distance generation means 10 for generating a moving distance LO per unit time corresponding to a predetermined manual feeding speed and a moving distance zero generation means 12 for generating a moving distance zero (0) per unit time for stopping manual feeding. The moving distance generation means 10 outputs a signal 100 and the moving distance zero generation means 12 outputs a signal 101. The moving distance generation means 10 is connected to a constant multiplication means 14 for selecting a constant (one of constants of usually 10 to 15 stages) for changing the feeding speed and multiplying the signal 100 by the selected constant to produce a signal 102. The constant multiplication means 14 is connected to an a contact point of a plus direction manual feed button switch 16 and an a contact point of a minus direction manual feed button switch 18. These button switches 16 and 18 are each normally connected to b contact points and are connected to the a contact points while the buttons are being pressed. Similarly, the moving distance zero generation means 12 is coupled with the b contact points of the button switches 16 and 18. In this case, an interlock (not shown) is provided for preventing the actuation of the two button switches 16 and 18 when the two button switches 16 and 18 are pressed at the same time. The button switches 16 and 18 output respective signals 103 and 104 to a subtracter 20 for subtracting the signal 104 from the signal 103, and the subtracter 20 outputs a subtraction result signal 105 to an acceleration and deceleration (+and-speed) processing part 22 for restraining an occurrence of a large acceleration or torque due to a step-form variation of the feeding speed by the on/off operation of the button switches 16 and 18 by using a suitable acceleration or deceleration method.
The acceleration and deceleration processing part 22 outputs a signal 106 to a position instruction value generator 24 for integrating the moving distances per unit time, instructed up to now to generate a necessary position instruction value, and the position instruction value generator 24 outputs a signal 107 to a position control part 26 for carrying out positional control of a control axis. In this case, the signal 105 is output from the subtracter 20 only in the manual operation mode. The above-described construction is provided for the first axis, and the same construction is formed for the second or third axis, FIG. 9 showing only the construction for the first and second axes.
There is shown in FIG. 10 the conventional position control part 26. In the position control part 26, a position sensor 30 for detecting the position of a turret 28 such as a bit holder sends a present position signal 108 to a subtracter 34 through a position sensing interface 32, and the subtracter 34 subtracts the present position signal 108 from the position instruction value 107 output by the position instruction value generator 24 and outputs a subtraction result signal 109 to a position control amplifier 36 for amplifying the output signal 109. The position control amplifier 36 outputs a signal 110 to a subtracter 42, and the subtracter 42 subtracts a signal 111 output by a tacho-generator 40 for detecting a rotating speed of a servo motor 38 from the signal 110 output from the position control amplifier 36 and outputs a subtraction result signal 112 to a speed control amplifier 44 for amplifying the output signal 112. The speed control amplifier 44 outputs a signal 113 to a subtracter 48. The subtracter 48 is connected to a current control amplifier 50, and a current detector 46 detects a current fed from the current control amplifier 50 to the servo motor 38 and outputs a detected current value to the subtracter 48. The subtracter 48 subtracts the current value detected by the current detector 46 from the signal 113 output by the speed control amplifier 44 and outputs a subtraction result signal 114 to the current control amplifier 50. The shaft of the servo motor 38 is coupled with a ball screw shaft 54 via a coupling 52, and a ball screw part 56 secured to the turret 28 is engaged with the ball screw shaft 54. Hence, by rotating the ball screw shaft 54, the turret 28 is moved to and fro in a direction shown by an arrow. Now, assuming that the control amplifiers 36, 44 and 50 are linear amplifiers, the turret 28 can be moved until the present position signal 108 finally becomes equal to the position instruction value 107.
Next, one embodiment of a tool offset setting for initial work processing using a numerically controlled (NC) lathe will be described as follows.
For the explanation, an axis parallel with the rotational central line of a job to be processed is defined as a Z axis and an axis perpendicular to the central line is defined as an X axis. A shift (.DELTA.Z=Z.sub.1 -Z.sub.0, .DELTA.X=X.sub.1 -X.sub.0) of an actual tool position (Z=Z.sub.1, X=X.sub.1) positioned by actually giving Z=0, X=0 and position instructions from a program origin (Z=Z.sub.0, X=X.sub.0) determined during programming is called a tool offset, and the tool offset is determined by an operator so that a previously formed cutting program may be used as it is without changing Z and X position instructions formed on the basis of the program origin within the cutting program for each separate job.
In order to determine tool offsets of tools to be used, the operator in place performs processing of the job mounted in a chuck by operation of the feed override switch and the manual feed button or operation of the pulse handle with attention to interference of the tools, and its dimension is measured by using slide calipers or the like and is input to the NC device by using keys on an operational panel. Hence, as in the case when initialising the NC lathe, when a number of tools are mounted or exchanged, this is a considerable number of work steps which places a burden on the operator. Therefore, nowadays, a tool edge measuring instrument is provided on the NC lathe in place of the job processing and the direct measurement of its dimensions. For obtaining the tool offset, the edge of the tool is moved near a sensor of the tool edge measuring instrument by the operation of the feed override switch and the manual feed button or the operation of the pulse handle, and then the tool offset setting in either a Z-axis or the X-axis direction is selected by a switch or the like to start a measuring cycle for moving the tool at a predetermined feeding speed. At the time when the tool edge contacts the sensor at this feeding speed, the NC device automatically calculates and sets the tool offset of the tool.
FIG. 11 illustrates the operation of the conventional NC device having the tool edge measuring function. Now, the operation is totally carried out in the manual operation mode. In FIG. 11, P.sub.H (Z.sub.H, X.sub.H), P.sub.1 (Z.sub.1, X.sub.1) and P.sub.S (Z.sub.S, X.sub.S) are a normal inoperative position of the tool, an intermediate position and an automatic measuring start position, respectively. First, by considering that there is no tool interference up to the intermediate position P.sub.1 (Z.sub.1, X.sub.1), a relatively quick feeding speed is selected by the feed override switch, and the tool edge is positioned to the intermediate position P.sub.1 (Z.sub.1, X.sub.1) by operating the manual feed button in a minus (-) Z-axis or minus (-) X-axis direction. In FIG. 11, a broken line indicates the shortest distance and a solid line shows an actual moving locus of the tool edge. Then, moving to the automatic measuring start position P.sub.S (Z.sub.S, X.sub.S) near the sensor, a slow feeding speed is selected by the feed override switch in order to pay attention to the tool interference, and the tool edge is positioned to the automatic measuring start position P.sub.S (Z.sub.S, X.sub.S) by operating the manual feed button in the - Z-axis or the - X-axis direction. In this case, since the tool offset setting in the Z-axis direction is supposed, the interval between the sensor and the tool edge is formed in the Z-axis direction. In turn, when the tool offset setting in the X-axis direction is assumed, the interval between the sensor and the tool edge is formed in the X-axis direction.
Next, either in the tool offset setting in the Z-axis direction, the button in the plus (+) or minus (-) Z-axis direction is selected and pushed or in the tool offset setting in the X-axis direction, the button in the + or - X-axis direction is selected and pushed, and the measuring cycle for moving the tool at the predetermined feeding speed is started. In this measuring cycle, the NC device detects the time when the tool edge contacts the sensor at the above-described feeding speed, and at this time, the tool position is accurately calculated to automatically determine the tool offset of the tool. In FIG. 11, one-dotted-lines indicate the motion of the measuring cycle.
Next, the conventional tool edge measuring operation will be described in connection with a flow chart shown in FIG. 12.
The NC device discriminates whether or not it is in manual operation mode in step S1. When it is discriminated that it is not in the manual operation mode, the operation is finished. When it is discriminated that it is in the manual operation mode, it is discriminated whether or not tool edge measurement is to be performed in step S2. When it is discriminated that the tool edge measurement is not being carried out, the operation is finished. When it is discriminated that the tool edge measurement is being performed, a positioning of the tool in the X-axis and Z-axis directions is carried out by operating the feed button and the pulse handle in order to set the tool offset in the X-axis and Z-axis directions. Then, it is discriminated whether or not a start button for the tool edge measurement in the Z-axis direction has been pressed in step S3. When it is discriminated that the start button for the tool edge measurement in the Z-axis direction has been pressed, it is discriminated whether or not a plus (+) direction is pressed in step S4. When it is discriminated that the + direction is pressed, a contact point in the + Z-axis direction is calculated and the tool offset in the + Z-axis direction is set in step S5. Next, it is discriminated whether or not the tool edge measurement is finished in step S6. When it is discriminated that the tool edge measurement is finished, the tool edge measurement is terminated. When it is discriminated that the tool edge measurement is not finished, the operation is returned to step S3. Further, when it is discriminated that the + direction is not pressed in step S4, a contact point in a minus (-) Z-axis direction is calculated and the tool offset in the - Z-axis direction is set in step S7. Then, the operation is moved to step S6 and the steps followed thereby are carried out. Also, when it is discriminated that the start button for the tool edge measurement in the Z-axis direction is not pushed in step S3, it is discriminated whether or not a start button for the tool edge measurement in the X-axis direction is pushed in step S8. When it is discriminated that the start button for the tool edge measurement in the X-axis direction is pushed, it is discriminated whether or not the + direction button is pushed in step S9. When it is discriminated that the + direction button is pushed, a contact point in the + X-axis direction is calculated and the tool offset in the + X-axis direction is set in step S10. Then, the operation is moved to step S6, as described above. In turn, when it is discriminated that the + direction button is not pressed in step S9, a contact point in the - X-axis direction is calculated and the tool offset in the - X-axis direction is set in step S11. Then, the operation is moved to step S6 and the steps followed thereby are carried out, as described above.
As described above, in the conventional NC device having the tool edge measurement function, the movable part holding the tool or the like is moved by the operation of the feed override switch and the manual feed button or the operation of the pulse handle. In the case of operation of the pulse handle, the feeding speed is very slow compared with the operation of the feed override switch and the manual feed button. Further, in an NC device such as a machining center for performing a position control of a movable part holding tools or the like by composing three axes, since the operator has only two hands, three pulse handles for the three axes can not be operated at the same time. The reason why such a problem concerning the operability can not be improved upon until now is as follows. That is, since the NC device recognizes the positions of the parts by numerical data, when the operator does not know the desired target position in terms of a sufficiently accurate numerical value, it is considered that a certain extent of operability sacrifice is permissible because of the nature of the NC device, and further, since a purpose can be accomplished simply by pushing a start button in a machine tool using the NC device when a cutting program used in quantity production is completed, complicated operation for the moving functions of the movable part at the time of the preparation of the above-described initial setting or the initial setting change do not need to be carried out by the operator. Further, in the NC lathe for controlling one turret by two axes, in order for the operator to quickly move the tool edge, problems arise because that is, it is difficult to operate the two manual feed buttons for the Z- and X-axis at the same time because he only has two hands. Namely, the operation of the two axis can be only performed separately, and the manual feeding speed for each axis can not be continuously changed by the feed override switch. As, at the present time, shortening of job processing time is fairly advanced and the ability to process the jobs of a variety of articles in a small amount of time is desired, the reduction of the time needed for the preparation of the initial setting and the initial setting change becomes very significant.